Past CA-36773 efforts to design a range of ErbB2 promoter-targeted therapeutics saw proof-of-concept progress but confronted translational challenges relating to their in vivo delivery and tumor bioavailability. Building upon our more recent discovery of drug-like small molecule inhibitors of ErbB2 promoter activity and transcriptional expression identified from high-throughput screening of approximately 2,000 structurally diverse anticancer compounds, this project's efforts will now focus on two primary objectives 1) defining and characterizing the ErbB2 promoter targets responsible for ErbB2 transcriptional silencing by these small molecule lead agents, and 2) validating, optimizing and advancing the preclinical development of the most promising of these small molecules or their structurally related analogs for the clinical treatment of ErbB2 over expressing cancers. Among the lead agents now being evaluated against ErbB2-dependent breast cancer models are the hydroxamic acid inhibitor of histone deacetylases (HDAC), trichostatin A (TSA, N8C-709238), a G/C-preferring minor groove DNA binder (NSC-58514), an atypical topoisomerase II inhibitor (NSC-176328), and several potent antitumor compounds with uncertain target mechanisms (NSC-131547, NSC-259968, NSC-321237) In our first set of specific aims, four different experimental approaches will be used to evaluate the activated vs. TSA-silenced ErbB2 promoter in ErbB2-dependent vs. ErbB2-independent breast cancer cell lines and in cell lines bearing ectopic and genomically integrated ErbB2 promoter-reporter constructs mutated in critical cis-acting regulatory elements. The overall goal of this first aim is to identify transcriptional and nucleosomal components thought to selectively drive ErbB2 overexpression and to pinpoint the ErbB2 promoter mechanisms most susceptible to targeted inhibition by small molecules. In the second set of specific aims, small molecule ErbB2 promoter and transcript inhibitingcandidates will be optimized for further clinical development on the basis of their in vitro and in vivo activities against ErbB2 overexpressing breast cancer models. Promising candidates emerging from an in vitro screen against a panel of 60 ErbB2-dependent and ErbB2-independent human breast cancer cell lines will be assessed for in vivo antitumor activity following parenteral administration into mice bearing implanted ErbB2-dependent or ErbB2-independent breast cancers. Efforts are also planned to improve the bioavailability and tumor-targeted uptake of selected candidates by encapsulation into anti-ErbB2 immunoliposomes (ILs), and these ErbB2 receptor- and promoter-targeted ILs agents will be evaluated in vivo for further clinical development.